1. Field of the Invention
This invention relates to the field of fluid pressure boosters such as negative pressure boosters, hydraulic pressure boosters and the like for boosting the input provided to an input means and outputting the boosted input using fluid pressure and particularly to the field of a fluid pressure booster in which the stroke of an input means is set extremely short, to ensure that fluid pressure can be outputted with a simple arrangement when the fluid pressure falls. Also, this invention relates to the field of a brake system in which the stroke of a brake operating member such as a brake pedal and the like is set extremely short to ensure that a brake can be actuated with a simple arrangement when fluid pressure falls.
2. Description of the Related Art
In order to obtain greater braking force with less pedal stepping force in conventional automobile brake systems, there have heretofore been employed fluid pressure boosters for generating a greater output by boosting the pedal stepping force with fluid pressure. As one of the fluid pressure boosters as stated above, there is a fluid pressure booster which is designed to gain a greater output by boosting the pedal stepping force with the negative pressure.
FIG. 10 is a sectional view showing a conventional ordinary negative pressure booster by way of example. As shown in FIG. 10, a negative pressure booster a comprises a front shell b, a rear shell c, a power piston member d, a diaphragm e, a power piston f, a vacuum chamber g, a working pressure chamber h, a valve body i, an input rod j, a valve plunger k, an atmospheric valve seat m provided for the valve plunger k, a vacuum valve seat n provided for the valve body i, a control valve disc o, a control valve p, passage holes q and r, an output rod s, a return spring t, a reaction disc u, a negative pressure inlet pipe v, and an atmosphere inlet port w.
In this conventional negative pressure booster a, negative pressure is kept being introduced into the vacuum chamber g via the negative pressure inlet pipe v. In the non-operating condition of the negative pressure booster a, further, the atmospheric valve seat m of the control valve p is kept into contact with the control valve disc o, which is slightly separated from the vacuum valve seat n or seated on the vacuum valve seat n (in this example shown, the control valve disc o is seated on the vacuum valve seat n), and the control valve p is in the non-operating condition. Therefore, the working pressure chamber h is cut off from the atmosphere and caused to communicate with the vacuum chamber g via the passage hole r, the gap between the control valve disc o and vacuum valve seat n, and the passage hole q. In this condition, the negative pressure is introduced into the working pressure chamber h or otherwise the working pressure chamber h is cut off any one of the atmosphere and vacuum chambers g. Moreover, a pressure slightly higher than the pressure in the vacuum chamber g facing the return spring t is introduced into the working pressure chamber h so that the control valve disc o may be seated on any one of the atmospheric valve seat m and vacuum valve seat n.
When a brake pedal (not shown) is stepped on out of the above condition, the input rod j is stroked forward (to the left in FIG. 10) and the atmospheric valve seat m separates from the control valve disc o when the control valve disc o is seated on the vacuum valve seat n or the atmospheric valve seat m immediately separates from the control valve disc o. In other words, the control valve p is switched over. Then the atmosphere is introduced from the atmosphere inlet port w into the working pressure chamber h via the gap between the control valve disc o and atmospheric valve seat m, and the passage hole r. As a predetermine difference in pressure is thus produced between the working pressure chamber h and vacuum chamber g, the power piston f including the power piston member d and the diaphragm e operates to generate an output. This output is then transferred to the master cylinder (hereinafter called MCY) of a brake (not shown) via the valve body i, the reaction disc u and the output rod s, whereby the MCY operates to generate brake pressure for operating the brake.
As the pressure in the working pressure chamber h increases, the output of the power piston f grows greater, thus making the valve body i move forward further, and the atmospheric valve seat m is brought into contact with the control valve disc o seated on the vacuum valve seat n. Accordingly, the atmosphere will not be introduced into the working pressure chamber h any further, so that the pressure in the working pressure chamber h becomes what corresponds to the input (the force related to the pedal stepping force) supplied to the input rod j. The output of the power piston at this time becomes what is obtained by boosting the pedal stepping force, which results in causing the MCY to generate brake pressure. Then the valve plunger k is brought into contact with the reaction disc u, which is subjected to elastic deformation because it is clamped between the valve body i and output rod s. The force generated by the elastic deformation of the reaction disc u is transmitted to the brake pedal as counterforce via the valve plunger k and the input rod j.
When the brake pedal is released, the input rod j and the valve plunger k both are moved back and the atmospheric valve seat m is brought into contact with the control valve disc o and further the control valve disc o separates from the vacuum valve seat n. Then the atmosphere introduced into the working pressure chamber h is discharged from the negative pressure inlet pipe v via the gap between the control valve disc o and vacuum valve seat n, the passage hole q and the vacuum chamber g. Consequently, all of the power piston f, valve body i and output rod s are moved back to take the non-operating position and the control valve p also takes the non-operating position.
Thus, this negative pressure booster makes a greater output obtainable with small pedal stepping force.
Recently, the stroke of the brake pedal in such a brake system as mentioned above has been desired to be contracted as much as possible. In the aforementioned conventional negative pressure booster, however, the valve body i is inevitably moved forward together with the forward movement of the power piston f as well as the output rod s when the output of the power piston f is produced in operation. Since the control valve p provided in the valve body i is also greatly moved forward, the input rod j necessarily produces a large stroke. Due to the loss stroke (the stroke of the MCY piston until the MCY actually produces the brake pressure) in the brake system ahead of the MCY, moreover, the valve body i, the power piston f and the output rod s are considerably moved forward. Consequently, the pedal stroke still remains large in the conventional negative pressure booster and this makes it impossible to meet the aforementioned demand for the contraction of the pedal stroke as much as possible.
The provision of the control valve (though not shown) for the power piston in any one of the conventional fluid pressure boosters designed for boosting the pedal stepping force with the fluid pressure causes the power piston to move forward considerably together with the control valve likewise, thus resulting in making greater the stroke of the input rod, that is, the pedal stroke.
Particularly in the case of braking (low speed reducing braking, that is, slow braking) in the low G zone, the idle stroke of the brake cylinder, master cylinder and booster out of the pedal stroke accounts for a large percentage and it is more difficult to shorten the stroke as the idle stroke is indispensable for preventing brake dragging.
Moreover, there is a fluid pressure booster wherein a control valve apart from a power piston is provided in parallel to a power piston within a housing (e.g., JP-A 9-164938). In this fluid pressure booster, the ends of a rocking lever fitted to an input rod are respectively coupled to the control valve and the power piston so that the ends thereof are capable of rocking. In other words, the input applied to the input rod is used to operate the control valve and the power piston via this lever. Therefore, since the lever is moved forward together with the stroke of the power piston during the operation, the stroke of the input rod still becomes larger. Moreover, the fluid pressure booster tends to become complicated in construction because the lever is fitted to the input rod, control valve and the power piston in such a manner as to be capable of rocking with a predetermined lever ratio and because the input of the input rod is used to operate and control the control valve and power piston with the lever ratio.
On the other hand, there is a full power brake system as a conventional brake system wherein the pedal stroke can be shortened. This full power brake system (though not shown) is different from the aforementioned negative or liquid pressure booster in that the brake is not actuated by activating MCY using the output of a power piston and then introducing the brake pressure generated by the MCY into a brake actuator. In the full power brake system, a brake valve for controlling supply and discharge of a working fluid under the control of a brake pedal without using the power piston and a brake actuator for producing the brake force are installed. Further, the brake is actuated by operating the brake valve to directly introduce the fluid pressure in a fluid pressure source into the brake actuator. In the full power brake system, since the brake valve is simply operated during the operation of the system, the pedal stroke can be relatively smaller but the problem is that the system becomes complicated to ensure the operation of the brake by stepping on the brake pedal when the fluid pressure falls.
Therefore, it is not so simple to apply the arrangement of the short pedal stroke in that full power brake to the fluid pressure booster having the power piston.